TOKYO -- North Korea, complaining it hasn't been given energy aid as promised, has slowed decommissioning work at its nuclear reactor, sources said Tuesday.

Citing unnamed sources, the Japanese news agency Kyodo said North Korea's moves to decommission its nuclear reactor at Yongbyon have slowed as delivery of about 75 percent of assistance agreed to in "six-party" talks has been completed but the other 25 percent remains held up.

In response, North Korea has slowed the pace of decommissioning work by cutting the number of nuclear fuel rods it is removing from the reactor from 15 per day to 15 per week, sources told Kyodo. About 80 percent of the 8,000 nuclear fuel rods have been removed from the reactor and placed in an adjacent water pond, officials say.

Japan has refused to join in the energy assistance to Pyongyang, saying it is first seeking the resolution of kidnapping cases of Japanese nationals by North Korean agents in the 1970s and 1980s, Kyodo reported.